.\" $Header$ -*-nroff-*-
.\" Purpose: ROFF man page for nces
.\" Usage:
.\" nroff -man ~/nco/man/nces.1 | less
.TH NCES 1
.SH NAME
nces \- netCDF Ensemble Statistics
.SH SYNTAX
nces [\-3] [\-4] [\-5] [\-6] [\-7]
[\-A]
[\-\-bfr
.IR sz_byt ]
[\-C]
[\-c]
[\-\-cb
.IR y1,y2,m1,m2,tpd ]
[\-\-cnk_byt
.IR sz_byt ]
[\-\-cnk_csh
.IR sz_byt ]
[\-\-cnk_dmn 
.IR nm,sz_lmn ]
[\-\-cnk_map 
.IR map ]
[\-\-cnk_min
.IR sz_byt ]
[\-\-cnk_plc 
.IR plc ]
[\-\-cnk_scl 
.IR sz_lmn ]
[\-D 
.IR dbg_lvl ]
[\-d 
.IR dim ,[
.IR min ][,[
.IR max ]]]
[\-\-dbl|flt]
[-F]
[--fl_fmt=fmt]
[\-G
.IR gpe_dsc ]
[\-g  
.IR grp [,...]]
[\-h]
[\-\-hdf]
[\-\-hdr_pad
.IR sz_byt ]
[\-L 
.IR dfl_lvl ] 
[\-l 
.IR path ]
[\-\-msa]
[\-N]
[\-n 
.IR loop ]
[\-\-no_cll_msr]
[\-\-no_frm_trm]
[\-\-no_tmp_fl]
[\-\-nsm_sfx
.IR grp_sfx ]
[\-O] [\-p 
.IR path ]
[\-\-ppc 
.IR var1 [,
.IR var2 [,...]]=
.IR prc ]]
[\-R]
[\-r]
[\-\-ram_all]
[\-t
.IR thr_nbr ]
[\-\-uio]
[\-\-unn]
[\-v 
.IR var [,...]]
[\-X 
.IR box ] 
[\-x]
[\-y 
.IR op_typ ]
.I input-files
.I output-file
.SH DESCRIPTION
.PP
.B nces
performs gridpoint averages of variables across an arbitrary
number (an 
.IR ensemble )
of input files, with each file receiving an
equal weight in the average.
Each variable in the 
.I output-file
will be the same size as the same
variable in any one of the in the 
.IR input-files ,
and all
.I input-files
must be the same size. 
Whereas 
.B ncra
only performs averages over the record dimension
(e.g., time), and weights each record in the record dimension evenly, 
.B nces
averages entire files, and weights each file evenly.
All dimensions, including the record dimension, are treated identically
and preserved in the 
.IR output-file .
.PP
The file is the logical unit of organization for the results of many
scientific studies.
Often one wishes to generate a file which is the gridpoint average of
many separate files. 
This may be to reduce statistical noise by combining the results of a
large number of experiments, or it may simply be a step in a procedure
whose goal is to compute anomalies from a mean state. 
In any case, when one desires to generate a file whose properties are
the mean of all the input files, then 
.B nces
is the operator to
use. 
.B nces
assumes coordinate variable are properties common to all of
the experiments and so does not average them across files.
Instead, 
.B nces
copies the values of the coordinate variables from
the first input file to the output file.
.SH EXAMPLES
.PP
Consider a model experiment which generated five realizations of one
year of data, say 1985.
You can imagine that the experimenter slightly perturbs the
initial conditions of the problem before generating each new solution.  
Assume each file contains all twelve months (a seasonal cycle) of data
and we want to produce a single file containing the ensemble average
(mean) seasonal cycle.  
Here the numeric filename suffix denotes the experiment number
(\c
.I not
the month):
.RS
nces 85_01.nc 85_02.nc 85_03.nc 85_04.nc 85_05.nc 85.nc
.br
nces 85_0[1-5].nc 85.nc
.br
nces \-n 5,2,1 85_01.nc 85.nc
.RE
These three commands produce identical answers.
The output file, 
.BR 85.nc ,
is the same size as the inputs files.
It contains 12 months of data (which might or might not be stored in the
record dimension, depending on the input files), but each value in the
output file is the average of the five values in the input files.
.PP
In the previous example, the user could have obtained the ensemble
average values in a particular spatio-temporal region by adding a 
hyperslab argument to the command, e.g.,
.RS
nces \-d time,0,2 \-d lat,\-23.5,23.5 85_??.nc 85.nc
.RE
In this case the output file would contain only three slices of data in
the 
.I time
dimension. 
These three slices are the average of the first three slices from the
input files.
Additionally, only data inside the tropics is included.

.\" NB: Append man_end.txt here
.\" $Header$ -*-nroff-*-
.\" Purpose: Trailer file for common ending to NCO man pages
.\" Usage: 
.\" Append this file to end of NCO man pages immediately after marker
.\" that says "Append man_end.txt here"
.SH AUTHOR
.B NCO
manual pages written by Charlie Zender and originally formatted by Brian Mays.

.SH "REPORTING BUGS"
Report bugs to <http://sf.net/bugs/?group_id=3331>.

.SH COPYRIGHT
Copyright \(co 1995-present Charlie Zender
.br
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

.SH "SEE ALSO"
The full documentation for
.B NCO
is maintained as a Texinfo manual called the 
.B NCO Users Guide.
Because 
.B NCO
is mathematical in nature, the documentation includes TeX-intensive
portions not viewable on character-based displays. 
Hence the only complete and authoritative versions of the 
.B NCO Users Guide 
are the PDF (recommended), DVI, and Postscript versions at
<http://nco.sf.net/nco.pdf>, <http://nco.sf.net/nco.dvi>,
and <http://nco.sf.net/nco.ps>, respectively.
HTML and XML versions
are available at <http://nco.sf.net/nco.html> and
<http://nco.sf.net/nco.xml>, respectively.

If the
.B info
and
.B NCO
programs are properly installed at your site, the command
.IP
.B info nco
.PP
should give you access to the complete manual, except for the
TeX-intensive portions.

.BR ncap2 (1), 
.BR ncatted (1), 
.BR ncbo (1), 
.BR ncclimo (1), 
.BR nces (1), 
.BR ncecat (1), 
.BR ncflint (1), 
.BR ncz2psx (1), 
.BR ncks (1), 
.BR nco (1), 
.BR ncpdq (1), 
.BR ncra (1), 
.BR ncrcat (1), 
.BR ncremap (1), 
.BR ncrename (1), 
.BR ncwa (1) 

.SH HOMEPAGE
The 
.B NCO
homepage at <http://nco.sf.net> contains more information.
